1. Field of The Invention
The present invention relates to an endless rectilinear motion guide unit, wherein a pair of lower and upper load-carrying trackways having different widths are formed on each side of a track rail member, viz., four trackways in all on both sides thereof and, on the inner sidewall of a slide unit are also formed the corresponding number of lower and upper load-carrying trackways for mating in size and position with said four load-carrying trackways of the track rail member, so that the slide unit, upon having been assembled in straddling relation with said track rail member with a plurality of cylindrical rollers being arranged in parallel with one another between the mating trackways, can freely and rectilinearly move on said track rail member with the desired load capacity ratio between the lower and upper trackways.
In more details, the present invention provides an endless rectilinear motion guide unit wherein in each of the opposing sides of the slide unit are provided two endless circulating passages having different sizes, viz., a longer passage having a larger cross section and a shorter passage having a smaller cross section, which are so arranged, as seen in a cross section thereof, that their longitudinal axes cross each other at right angles, while the longer circulation passage having a larger cross section encompasses, within the loop, the shorter circulation passages having a shorter cross section, but the lengths of the load-carrying trackway surfaces of said two circulation passages are the same.
2. Prior Arts
German Utility Model Application No. 1971845 and Japanese Patent Application Publication No. 24646-1987 each disclose and endless rectilinear motion guide unit having four trackways along and through which a plurality of parallel-arranged cylindrical rollers move.
However, the prior units have the following inherent disadvantages:
In case of the German Utility Model, for example, two endless circulation passages having different sizes are formed on each side of the slide unit, which are so arranged that a longer passage having a larger cross section encompasses within the loop, a shorter passage having a smaller cross section but due to the difference in length of the load-carrying trackway surfaces, load capacities of the two passages differ from each other as the result with the shorter one having a shorter effective life, so that the prior art unit can find only limited utility.
In case of the Japanese patent application, two endless circulation passages are provided in each of the opposing sides of the slide unit, which are linked each other like a chain so that through the load-carrying trackways of the two passages are the same in length, the longitudinal length as a whole of the associated endless circulation passages becomes greater, inevitably resulting in an enlargement of the unit as a whole.
Furthermore, each of the above-mentioned prior rectilinear motion guide units has limited utility due to the limited load capacity, particularly for use in the case where a greater load capacity is required in the downward direction.